Preparation Of Graphene-based Photocatalysts And Their Photocatalytic Water Splitting Performance

Photocatalytic water splitting is a clean and sustainable technology that uses solar energy to break down water into hydrogen,which showing great potential for solving the growing energy shortage and achieving carbon emission reduction goals.Nevertheless,the design and exploitation of new high-efficiency photocatalysts,the investigation of their photocatalytic water decomposition performance and the uncovering of their response models are still the primary key issues to be addressed in the industrial application of photocatalytic water splitting technology.Metal sulfide,chalcogenide and other classical single-phase catalysts are widely used in photocatalysis,but there are disadvantages such as easy compounding of photogenerated carriers and poor visible light response.Graphene is an excellent electron acceptor and conductor due to its large specific surface area and good optical,electrical,and thermal stability,and can be easily used as a carrier to form composite materials with excellent photocatalytic activity with other semiconductors.Based on this,this thesis explores the modification study of GO on monometallic sulfide hemi-dissolution catalysts,then on multi-metallic sulfide hemi-dissolution catalysts,and finally on chalcogenide all-dissolution catalysts,providing a strategy to realize the large-scale application of decomposing water for hydrogen production.Three graphene-based composite photocatalysts,GO/In₂S₃,GO/CdIn₂S₄ and GO/Rh-STO,were designed and prepared,respectively,and the microscopic states,physicochemical properties,photocatalytic water decomposition performance and photogenerated electron-hole pair separation and migration mechanisms of the composites were investigated.As follows:（1）The GO/In₂S₃ heterogeneous structure was successfully constructed by simple hydrothermal method with in situ growth of flower spheres of In₂S₃on GO nanosheets,which greatly improved the charge separation and migration,light absorption wavelength range,and thus the photocatalytic water splitting hydrogen activity.The photocatalytic results showed that the photocatalytic water splitting activity of GO/In₂S₃ heterostructure was much higher than that of pure In₂S₃,and the rate of H₂production of the best GO/In₂S₃ sample was as high as 940μmol·h^-1·g^-1,which was about 2.2 times higher than that of pure In₂S₃(430μmol·h^-1·g^-1).Meanwhile,the performance of the GO/In₂S₃ heterostructure remained basically unchanged when it was subjected to cyclic water splitting hydrogen tests for 60 hours,indicating that the GO/In₂S₃ heterostructure has excellent stability and reusability.（2）A binary flower ball CdIn₂S₄ was grown in situ on GO nanosheets by hydrothermal method,and the GO/CdIn₂S₄ heterostructure was successfully constructed,which greatly improved the charge separation and migration,light absorption wavelength range,and thus the photocatalytic water splitting hydrogen activity.The photocatalytic results showed that the photocatalytic water splitting hydrogen activity of GO/CdIn₂S₄ heterostructure was much higher than that of pure CdIn₂S₄.The the rate of H₂ production of the best GO/CdIn₂S₄ sample was as high as2.48 mmol·h^-1·g^-1,which was about 2.5 times higher than that of pure CdIn₂S₄(1.01mmol·h^-1·g^-1).Meanwhile,the cyclic water splitting hydrogen was tested for a continuous period of 16 hours,and its performance remained basically unchanged,indicating that the GO/CdIn₂S₄ heterostructure has excellent stability and reusability.（3）A novel GO/Rh-SrTiO₃ nanocomposite was synthesized by a simple hydrothermal method by combining heterostructure construction technique and active site modification technique.The results of photocatalytic experiments show that the champion GO/Rh-SrTiO₃ nanocomposite exhibits the superior photocatalytic overall water splitting performance with the H₂ evolution rate of 55.83μmol?g^-1?h^-1 and O₂production rate of 23.26μmol?g^-1?h^-1,realizing a breakthrough from zero with respect to the single-phased STO under visible light（λ≥420 nm）.At the same time,it was tested for cyclic water splitting for a continuous period of 16 hours,and its performance remained basically unchanged,indicating that the GO/Rh-SrTiO₃ nanocomposite has excellent stability and reusability.More importantly,a series of characterizations results showed that improving significantly photocatalytic performance originated mainly from construction of heterostructure and more active sites rooted in Rh metal.Furthermore,the possible photocatalytic reaction mechanisms and transport behaviors of charge carriers are revealed in depth.The present work provides an effective strategy of heterostructure construction to improve solar utilization through expanding vastly visible light response ranges from traditional UV photocatalysts.